1. Field of the Invention
The present invention relates to a fixing apparatus, within an image forming apparatus, for thermal fusion-pressing a to-be-fixed toner on a recording medium in a copying machine, printer, facsimile equipment, etc., and, by doing so, fixing the toner to the recording medium.
2. Description of the Related Art
This type of fixing apparatus has a fixing roller and pressure applying roller set in pressure contact with the fixing roller and, by feeding a toner-image-transferred recording medium past a nip between the fixing roller and the pressure-applying roller, the toner is thermally-fused to the recording medium and is fixed onto it.
However, a color image transferred onto the recording medium involves a greater toner quantity and is required to meet better color reproduction or light transmission in the case of the medium being an OHP and, therefore, a toner of lower fusion viscosity is used.
In this situation, the fused toner is liable to be deposited onto the surface of the fixing roller and tends to cause xe2x80x9coffsettingxe2x80x9d.
Further, an added adhesion force acts between the toner and the fixing roller and it is difficult to separate the recording sheet from the fixing roller. This causes xe2x80x9cwrappingxe2x80x9d of the sheet onto the fixing roller.
In order to lower such an adhesion force between the fixing roller and the toner, a means is adopted, for example, for coating a silicone oil on the surface of the fixing roller.
In this case, however, an oil coating mechanism is required, thus necessitating oil refills, which increases the costs.
In the fixing apparatus for fixing a color image, the surface of the fixing roller is covered with a layer of rubber and, against the rubber layer of the fixing roller, a pressure applying roller made of metal is pushed with a nip set in an upwardly directed state, whereby the sheet passing through the nip is delivered in a downwardly directed state so that the sheet is separated and hence prevented from being xe2x80x9cwrappedxe2x80x9d onto the fixing roller.
If, however, the rubber layer is provided on the surface of the fixing roller, heat conduction from a heat source in the fixing roller is lowered and a longer warming-up time is required to reach a predetermined fixing temperature. In the color image forming apparatus, the reduction of the warming-up time is considered to be important from a standpoint of energy saving.
In a hard type of fixing roller having no rubber layer, a recording sheet is caused to be separated from the fixing roller with the use of a separating claw.
In the prior art, the separating claw is abutted against the fixing roller in the neighborhood of an exit side of the fixing nip and, since the sheet is separated at an abrupt angle, the scratching of an image by the separating claw is left as a mark and the fixing roller is injured and, as a result, a resultant image is lower in quality.
Where use is made of such a separating claw, the warming-up time of the fixing roller is fast but it is difficult to separate the recording sheet Properly. As a result, it is difficult to achieve a better trade-off between the separation of the recording sheet and a shortening in the warning-up time.
The present invention is achieved with the above in view and is directed to a fixing apparatus and image forming apparatus which can achieve a trade-off between the separation of a medium and a shortening in a warming-up time.
A fixing apparatus of the present invention comprises a fixing device having a fixing roller and pressure applying roller set in pressure contact with the fixing roller and, by feeding a developing agent image-transferred medium past a nip between the fixing roller and the pressure applying roller, fixing the developing agent image to the medium and a separating device having a forward end set in abutting contact with an outer peripheral surface of the fixing roller and separating the medium which is fed past the nip from the fixing roller, wherein the forward end of the separating device abuts against the outer periphery of the fixing roller in a range of a distance corresponding to xe2x85x9 to ⅓ of a full outer periphery length which is spaced from a center of the nip along the outer periphery of the fixing roller.
Further, an image forming apparatus of the present invention comprises an image carrier for carrying an electrostatic latent image, an image forming device for forming an electrostatic latent image on the image carrier, a plurality of developing devices for supplying developing agents of respective colors onto the electrostatic latent image formed by the image forming device to effect color development, a transferring device for transferring the developing agent image developed by the corresponding developing device, a fixing device having a fixing roller and pressure applying roller set in pressure contact with the fixing roller and, by feeding the color developing agent image-transferred medium past a nip between the fixing roller and the pressure applying roller, fixing the color developing agent image to the medium, and a separating device having a forward end abutting against an outer peripheral surface of the fixing roller to separate the medium which is fed past the nip from the fixing roller, wherein the forward end of the separating device abuts against the outer peripheral surface of the fixing roller in a range of a distance corresponding to a full outer periphery length of the fixing roller which is spaced from a center of the nip along the outer periphery of the fixing roller.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.